Polyphase brushless DC motors apply separate currents to stator windings of the motor in sequential order to produce torque-inducing flux for causing motion in a magnetic or ferromagnetic rotor of the motor. Typically, DC currents are alternatively applied to different stator windings to create current paths in a synchronized fashion to produce different magnetic flux orientations that produce torque on the rotor, and thus causing its rotational movement.
In order to ensure that current is applied to the proper motor phase to set up the proper flux generating current path, it tends to be advantageous to know the position of the rotor such that the windings may be energized in such a way that maximum torque is provided to the rotor. This may be particularly valuable when the motor is initially starting up and the rotor is stationary.